There are two major classes of contact lens disinfection systems: multipurpose disinfecting solutions (MPDS) and hydrogen peroxide systems. Hydrogen peroxide-based systems are often preferred, due to its better kill of bacteria, yeast, and fungi,preservative-free packaging, low user sensitivity to the active disinfection agent, and neutralization of the disinfection agent to natural by-products, e.g., water and oxygen.
Literature studies have shown that the contact lens surface typically harbors scores of different microbial species and viruses at the end of a wearing cycle. Of course, the specific species (and numbers of isolates of each species) vary from individual to individual and even between the two eyes. To standardize disinfection testing, the FDA (and industry) have adopted two types of testing; the “stand alone” test and the “regime” test. These two tests use strains of 3 bacterial species (Staphylococcus aureus, Pseudomonas aeruginosa, and Serratia marcesens) and a strain of Candida albicans and Fusarium solani. A minimum reduction in CFU at the end of disinfection time must be achieved for “adequate” disinfection to pass the regulatory test. All approved disinfection systems, including both one-step or two-step hydrogen peroxide systems (described further below), must pass these criteria. More complete killing during the disinfection process of troublesome microorganisms, e.g., yeast, fungi, and amoeba, will provide the consumer a reduced chance of infection (better safety) due to these micro-organisms.
Two common peroxide disinfection processes exist, so-called one-step and two-step peroxide systems, where the primary difference lies in when the catalyst is introduced into the peroxide solution. In a one-step peroxide system, the catalyst and peroxide are introduced at roughly the same time, whereas in the two-step system the catalyst is introduced much later—towards the end of a disinfection phase, i.e., well after the peroxide is introduced. The two-step system may more completely disinfect, i.e., has a greater kill rate because full strength hydrogen peroxide is present for much longer period of time, but requires the second step of introducing the catalyst to neutralize peroxide to a safe level, and the additional time necessary for neutralization. An additional draw back of the two-step system is a user may forget to introduce the catalyst, and accidently insert a lens with significant amounts of peroxide leading to increased discomfort and potential injury. The one-step system has the benefit of disinfecting and neutralizing at the same time, shortening the time needed before wearing the lenses and removing the potential of forgetting to introduce the catalyst. However, the one-step system does not have as high a kill rate as the two-step system because the one-step system, by design, immediately begins neutralizing the hydrogen peroxide, reducing capacity, over time, to kill bacteria, fungi, and or amoeba. One-step systems effectively reduce fungal microorganisms (e.g., C. albicans and A. brasiliensis) much greater than the acceptable level (e.g, ≧1-log kill); however, they may not as effectively reduce other microorganisms (e.g., Acanthamoeba), though there are no standardized acceptable levels at this time. The one-step hydrogen peroxide system is widely used as a lens disinfecting system today, and preferred by many users because of its superior killing efficacy as compared to non-hydrogen peroxide systems. Additional information can be found in C. Hildebrandt, D. Wagner, T. Kohlmann and A Kramer, In vitro analysis of the microbicidal activity of 6 contact lens care solutions, BMC Infectious Diseases 2012 12:241-253.